Display screen or portion thereof with a graphical user interface



The FIGURE is a front view of a display screen or portion thereof with a graphical user interface.

The outermost broken line rectangle illustrates a display screen or portion thereof. The remainder of the broken lines illustrate portions of the graphical user interface. The broken lines form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 